Problem: Solve for $z$ : $-20 = -4 + z$
Explanation: Add $4$ to both sides: $ \begin{eqnarray} \\ \hphantom{-20 {+ 4}} &\hphantom{=}& \hphantom{z} \\ -20 &=& -4 + z \\ \\ {+4} && {+4} \\ \end{eqnarray} $ $ \begin{eqnarray} \\ -20 {+ 4} &=& z \\ \end{eqnarray} $ Simplify. $ z = -16$